The present invention relates to an electronically programmable calculator with a memory package comprising a load/unload mechanism for a plurality of memory packages.
An electronically programmable calculator with a memory package and a load/unload mechanism for a plurality of memory packages, e.g., RAM cards or RAM packages is conventionally known. In this calculator, all the addresses of respective memory areas of the plurality of memory packages loaded into the mechanism are considered as a continuous, single address area, and a program or variable data can be written in the address area.
With an electronically programmable calculator of this type, in the program data setting mode, continuous absolute addresses are assigned to all the memory areas of a plurality of, e.g., loaded RAM cards which are considered as a single address area. For this reason, once a program or variable data is written in the memory area, the calculator can only be used with the RAM card which define the continuously determined data, and cannot be used with RAM cards of different memory capacities. More specifically, for example, one of a pair of RAM cards each having a capacity of 4 kB cannot be replaced with a RAM card having a smaller capacity of 1 kB or 2 kB.
Even though it is determined that the memory content of the memory package is partially erased, the abnormal portion cannot be detected. Therefore, unless all the data, such as a stored program or variable data, is cleared, the calculator cannot be switched to the execution mode, resulting in a time-consuming and ineffective operation.
In calculators requiring no specific type of operator, even though the memory packages are not loaded or are mis-loaded, a means for signalling a malfunction is not provided as in the above case, resulting in inconvenience. In addition, since the calculator cannot be switched to the execution mode, it lacks reliability. For this reason, strong demand has arisen for development of a mechanism for checking if the memory packages are correctly loaded or storage contents are normal.